The present embodiment relates generally to a relative permeability modifying polymer for use with spacer fluids for introduction into a subterranean zone penetrated by a well bore.
While drilling oil and gas wells, a drilling fluid is circulated through the string of drill pipe, through the drill bit and upwardly to the earth's surface through the annulus formed between the drill pipe and the surface of the well bore, thereby cooling the drill bit, lubricating the drill string and removing cuttings from the well bore.
When the desired drilling depth of the well is reached, another “performance” fluid, such as a slurry containing a cement composition, is pumped into the annularspace between the walls of the well bore and pipe string or casing. In this process, known as “primary cementing,” the cement composition sets in the annulus, supporting and positioning the casing, and forming a substantially impermeable barrier, or cement sheath, which isolates the casing from subterranean zones.
A spacer fluid is a fluid used to displace one performance fluid, such as a drilling fluid, in a well bore before the introduction into the well bore of another performance fluid, such as a cement slurry. Spacer fluids are often used in oil and gas wells to facilitate improved displacement efficiency when pumping new fluids into the well bore. Spacer fluids are also used to enhance solids removal during drilling operations, to enhance displacement efficiency and to physically separate chemically incompatible fluids. For instance, in primary cementing, the cement slurry is separated from the drilling fluid and partially dehydrated gelled drilling fluid may be removed from the walls of the well bore by a spacer fluid pumped between the drilling fluid and the cement slurry. Spacer fluids may also be placed between different drilling fluids during drilling fluid change outs or between a drilling fluid and a completion brine.
It is understood that the well bore may pass through zones which produce water instead of hydrocarbons. Besides being highly undesirable during the production phase of a well, water producing zones can cause problems in the well bore with certain completion activities.
Recently, wells in the production phase have been successfully treated with compounds known as relative permeability modifiers, which decrease the co-production of water with hydrocarbons by reducing the flow of water through hydrocarbon producing formations, yet have little or no effect on the permeability of the formations with respect to hydrocarbons. However, it is desirable to curb water production as early as possible in the life of a well, and to produce more effective relative permeability modifying compositions.
Thus, what is needed is a method and composition for modifying the permeability of water producing zones by the use of a relative permeability modifying composition in a spacer fluid.